1. Field of the Invention:
The present invention relates to a radiation detector which employs a very small radiation sensor capable of conducting a radiation energy spectrum analysis or a very small radiation sensor array for use in X-ray diagnostic equipment or a nondestructive inspection device, as well as to a method of manufacturing such a radiation detector.
2. Description of the Prior Art:
FIG. 10 shows the absorption mechanism in the photoelectric effect of radiation. When radiation 51 is incident upon an atom 52, of the various types of orbital electrons, the K-shell electron 53 is the one which mainly absorbs the radiation 51. After absorbing the radiation, the K-shell electron moves outward from its orbit as an excited electron 54. This generates a pair consisting of several electrons and holes in a semiconductor, and a number of photons of radiation can be detected by counting the current or voltage pulses generated by the electron-hole pairs. An electron with an orbit outward of the K-shell moves into the orbit of the K-shell to make up for the K-shell electron 53. When an electron in an outer orbit enters the K-shell, energy which represents the difference in orbital energies is emitted as a K-shell characterized X-ray 56.
FIG. 11 shows this phenomenon taking place in a semiconductor radiation sensor. The semiconductor radiation sensor shown in FIG. 11 is of an all depletion layer type. As radiation is absorbed within a semiconductor radiation sensor 55, an excited electron 54 and a K-shell characterized X-ray 56 are generated. The excited electron 54 loses most of its energy within the semiconductor crystal. However, when the K-shell characterized X-ray 56 is generated in the vicinity of the surface of the crystal, it is often caused to escape from the crystal. This phenomenon is called a K-shell characterized X-ray escape 57. When this occurs, the charges generated in a detector are reduced, reducing the height of the detector output pulses. FIG. 12 indicates this phenomenon using the output pulse height. A reference numeral 58 in FIG. 11 denotes an electrode of the semiconductor radiation sensor. FIG. 12a shows the number of photons with respect to the energy of the incident radiation. FIG. 12b shows the actually obtained distribution of the height of pulses output from the semiconductor radiation sensor when radiation having a one-component energy E is incident thereon. In an actual measurement, the output pulse is divided into two pulse groups: one having a height corresponding to the incident energy E and the other having a height corresponding to the energy E-Ei (where Ei is the bound energy of the K-shell electron).
Thus, when the incident one-component radiation energy generates two energy groups respectively represented by a pulse group having a height corresponding to the incident radiation energy and a pulse group caused by the K-shell characterized X-ray escape and having a height corresponding to an energy lower than the incident radiation energy, errors occur when the energy of a plurality of X-rays is to be measured. Further, the K-shell characterized X-ray may cross the boundaries between adjacent sensors in a sensor array and be incident upon adjacent sensors, causing signal cross talk.